The invention pertains more specifically to the detection of pathological cells such as micrometastases which can diffuse spontaneously after a surgical intervention, especially after the ablation of a cancerous organ, or of lymphocyte cells infected by viruses.
The early detection of micrometastases makes it possible to evaluate the risks of dissemination and onset of secondary cancers. The difficulty in the detection of such micrometastases stems from the small amount of cells present in a blood specimen.
The early detection of lymphocytes infected by viruses enables indirect and early detection of viral diseases.
In order to separate such rare events, it has been proposed in the prior art to first perform cell labeling. Specifically, it has been proposed to specifically affix the cancerous cells to magnetic balls. Use has also been made of cell sorters or the PCR (Polymerase Chain Reaction) method. These methods are time consuming and can not be routinely performed.
Also proposed in PCT patent WO 91/014318 was a process for the separation of different living cells, such as pancreas islet cells and acinar cells, using a composition comprising a metabolically inert water-soluble substance which regulates the density, osmolarity and pH, a physiological cold storage solution containing viscosity modifiers that increase the viscosity and impermeability agents with osmotic action that destroy the edemas induced by the cold, all contained in a medium capable of maintaining the viability of the cells. The solutions are combined to form a first solution having a density greater that that of the two types of cells in their natural state but lower than that of the second type of cells after incubation in this solution, as well as a second solution having a density lower than that of the two types of cells. Separation is produced by allowing the system to remain in the resting state or by performing centrifugation.
C. H. Zierdt described in “Development of a lysis-filtration blood culture technique”, Journal of Clinical Microbiology, Vol. 5, No. 1 1977, pages 46-50, a culture system that retains cells on filtration membranes. The biological specimen is subjected to the action of a lysis solution. The filter is then washed in order to recover the cells retained by the filter.
U.S. Pat. No. 4,751,179 describes a method for the determination of different populations of leukocytes in the blood.
Such solutions are relatively difficult to implement because of the various artifacts inherent in these processes. One of the problems stems, for example, from the agglomeration of balls and the masking of the cells fixed on the balls, by the excess balls. This method is therefore not applicable in a satisfactory manner because it impedes access to the morphology of the cells.